the blank final field factors may not have been initialized

Q1: why we should initialize final field before completion of new instance?

　　final means no changeable in java enviroment, the java compiler urges us follow the security violation.

Q2: how to resolve the error above?

　　actually, it is because factors perhaps refer to passed parameter.

     so , keeping a good habit to add the prefix 'this.' is good manner to resolve the error.

　　this.factors = Arrays.copyof....